Prolonged Heat Exposure in Cystic Fibrosis Can Lead to Metabolic Alkalosis

In patients with cystic fibrosis, prolonged exposure to heat can lead to chloride-deficient metabolic alkalosis as a result of a loss of electrolytes through sweat, according to a case report published in the Annals of Internal Medicine.

Chloride-deficient metabolic alkalosis usually has an obvious cause, but can be more complicated in patients with cystic fibrosis who have excessive chloride content in sweat. Researchers illustrated a rare cause of metabolic alkalosis in a 32-year-old man with known cystic fibrosis who presented with generalized weakness, fatigue, and failure to thrive for several days.

When examined, the patient was severely volume-depleted with hypotension and orthostatic blood pressure changes, subjective weight loss, and decreased skin turgor. Laboratory testing revealed severe metabolic alkalosis: CO2, 50 mmol/L; chloride, 70 mmol/L; sodium, 126 mmol/L; potassium, 2.1 mmol/L; magnesium, 0.78 mmol/L; blood urea nitrogen, 6.43 mmol/L; and creatinine, 61.88 μmol/L (0.7 mg/dL). Spot urine testing showed a sodium level of 10 mmol/L, a chloride level <10 mmol/L, and a potassium level of 26 mmol/L.

The patient did not report any nausea, vomiting, or diarrhea, and did not report having taken any diuretics. He had recently started working as a painter and complained that painting under the hot roof in summer “was killing him.” His symptoms and metabolic abnormalities resolved with intravenous saline, and he was discharged.

Thus, patients with cystic fibrosis can have massive losses of sodium chloride that can lead to extracellular volume contraction and produce metabolic alkalosis. Furthermore, extracellular volume contraction causes secondary hyperaldosteronism, which leads to hypokalemia from potassium wasting in both sweat and urine.

“This patient illustrates how sweat can be an important loss of electrolytes that can occasionally lead to chloride-deficient metabolic alkalosis in patients with cystic fibrosis,” the researchers concluded.


Ghimire S, Yerneni H, Oyadomari TA, Sedlacek M. Metabolic alkalosis and cystic fibrosis: a case report [published online June 2, 2020]. Ann Intern Med. doi:10.7326/l20-0038